The present invention relates to simultaneously writing multiple data tracks on an optical medium such as an optical tape.
The high capacity of optical recording media results from the small size and spacing of marks recorded in the data tracks and from the close spacing of tracks next to each other. In order to accurately record and read closely-spaced tracks, optical recording systems rely on high-precision servo systems. Preformatted patterns on the media surface are used to generate some of the required servo positioning signals. For example, replicated grooves or guide tracks in an optical disk substrate are commonly used to generate tracking signals (see Optical Recording, a Technical Overview, Alan Marchant, 1990, p. 172). The optical head includes a closed-loop servo system that follows the guide track while recording or reading data tracks disposed on the guide track or in an adjacent unmarked area. One guide track is provided for each possible data track.
Preformatted guide tracks are also useful for registering recorded marks on other types of optical media, e.g. optical tape (U.S. Pat. Nos. 4,884,260 and 5,989,671) and optical card (U.S. Pat. No. 5,053,610). Preformatted guide tracks provide a means for reducing cross-track run-out during optical data recording. But because of residual run-out, the preformatted guide tracks do not define the optimal path for tracking recorded data. Furthermore, prior art methods for servo control functions require format characteristics that reduce data capacity, especially when implemented for multi-track optical recording.
It is an object of this invention to improve track-following accuracy for data readout in an optical recording system that simultaneously records and reads multiple data tracks. It is a further object of this invention reduce the fraction of the media area dedicated to servo-control information on an optical recording medium used for simultaneously recording and reading multiple data tracks.
This object is achieved by a method for multi-track optical data recording, comprising the steps of:
a) providing an optical recording medium that includes a plurality of parallel, preformatted guide tracks, with sufficient space between adjacent guide tracks for recording a plurality of data tracks;
b) providing relative motion between the optical recording medium and an optical head in a direction generally parallel to the guide tracks;
c) imaging a guide track onto a detector array disposed relative to the optical recording medium, generating a first tracking error signal representing the cross-track displacement of the guide track relative to the optical head, and driving a closed-loop servo system to reduce the first tracking error signal; and
d) simultaneously recording a band of data tracks in the unpreformatted space adjacent to the guide track and one or more control tracks parallel to the data tracks.
The present invention has as an advantage that neighboring bands of data tracks recorded at different times are positioned with a high degree of positional accuracy and parallelism relative to the prior art. Increased positional accuracy and parallelism permits the data bands to be recorded closer together with less unused guard space, thus increasing the storage capacity of the recording medium.
The present invention further provides accurate servo signals associated with track position and data timing that are independently optimized for writing and reading data. Independent optimization of the servo functions assures optimum performance of the recording system in both operational modes.
A feature of the present invention is that patterns required for servo signals, clock synchronization, data addresses, and other format overhead may be concentrated on the medium and kept separate from data tracks, permitting higher speed recording by the data channels.